The invention relates to flame-emission photometric apparatus and, in particular, to precision-oriented improvements in the monochromator and in the sample changers used with such apparatus.
As is known spectrometric analysis can be achieved in a variety of ways. However, the present invention is concerned with the widely-used flame emission technique in which a liquid sample is aspirated into a flame. The resulting spectral line emission is isolated in a monochromator and passed to a phototube for producing a measurable electrical signal. This technique is considered, at least for present purposes, simpler, more effective and more precise than other techniques such, for example as the neutron activation methods used by some investigators.
I further should be recognized that the present invention has resulted primarily to permit extremely precise measurements of cesium present in the ocean or in its sediments and its organisms. Even so, as will be readily apparent, the use or applications of the present apparatus and its measurement techniques is by no means limited to the study of cesium or even to the trace amount measurements which have complicated the cesium studies.
The study of cesium and particularly the study of typical cesium concentrations in the ocean is a matter of considerable significance although, apparently, for a long time cesium has been treated as a minor alkali metal with relatively little effort directed toward its precise determination. For example, text data relating to typical cesium concentrations, over the past decades has demonstrated significant variations and it is quite clear that the data variations have been due primarily to the lack of precision in the analytical apparatus and methods. The need for advancing the art of measuring the alkali metal cesium has been recognized and described in a technical paper "Flame Photometer Specialized For Cesium" T. R. Folsom, C. Sreekumuran, W. E. Weitz, Jr., and D. A. Tennant, Applied Spectroscopy, 22 (2), March/April 1968, as well as a U.S. Patent "Flame Photometric Method and Apparatus for Quantatively Analyzing Material" Folsom, Weitz and Tennant, U.S. Pat. No. 3,588,257 issued June 28, 1971. However, even the more precise method described in these publications has proven somewhat inadequate. For example, their use has failed to disclose any statistically significant variation of cesium in the ocean even though it seems quite apparent that movement of terrestrial detritus through the ocean over a geological timescale should give rise to some differences of local concentrations of this very "rare" alkali metal.
Another matter of more practical concern is the fact that in recent years traces of the radioactive nuclides of cesium have shown up as fallout all over the world. Moreover, there now is evidence that large amounts of radioactive cesium are and will be accumulating in nuclear wastes which, accidently or otherwise, will find its way into the ocean where it will be of very real concern, particularly to marine food supplies. Manifestly, it is of considerable importance to know just how cesium traces have been distributed in the ocean over geological periods. Such analytical procedures as have been available have proven entirely too inadequate to produce reliable, realistic data.
One reason for the difficulties experienced in the measurements of cesium is the fact that this material occurs in the ocean only in very small traces mixed with much larger amounts of alkali metals. For example, the following table indicates the concentration of natural alkali metals present in sea water;
Table 1. ______________________________________ Natural alkali metals present in sea water. Alkali Symbol Approximate Concentration (g/) ______________________________________ cesium Cs 0.3 rubidium Rb 120 lithium Li 170 potassium K 380,000 sodium Na 10,500,000 ______________________________________
As is obvious from the above table, any study of cesium involves the measuring of this element in microgram amounts in the presence of millions of times this amount of other elements that behave as chemicals or, at least, somewhat similarly to chemicals. Reliable measurements of these microgram amounts requires a precision and reproducibility well beyond any presently known techniques.